This invention relates to communication systems and methods and more particularly to a system and method which provides for broadband information communication between processor-based systems through a centralized communication array using adaptive time division duplexing.
In the past, information communication between processor-based systems, such as local area networks (LAN) and other general purpose computers, separated by significant physical distances has been an obstacle to integration of such systems. The choices available to bridge the physical gap between such systems have not only been limited, but have required undesirable tradeoffs in cost, performance, and reliability.
One group of historically available communication choices includes such solutions as the utilization of a standard public switch telephone network (PSTN) or multiplexing signals over an existing physical link to bridge the gap and provide information communication between the systems. Although such solutions are typically inexpensive to implement, they include numerous undesirable traits. Specifically, since these existing links are typically not designed for high speed data communication, they lack the bandwidth through which to communicate large amounts of data rapidly. As in-building LAN speeds increase to 100 Mbps, the local PSTN voice grade circuits even more markedly represent a choke point for broadband metropolitan area access and therefore are becoming a less and less desirable alternative. Furthermore, such connections lack the fault tolerance or reliability found in systems designed for reliable transmission of important processor-based system information.
Another historically available group of communication choices is found at the opposite end of the price spectrum than those mentioned above. This group includes such solutions as the utilization of a fibre optic ring or point to point microwave communication. These solutions are typically cost prohibitive for all but the larger users. The point to point systems require a dedicated system at each end of the communication link which lacks the ability to spread the cost of such systems over a plurality of users. Even if these systems were modifiable to be point-to-multipoint, to realize the economy of multiple system use of some system elements, the present point-to-point microwave systems would not provide broadband data services but rather traditional bearer services such as T1 and DS3. Furthermore these systems typically provide a proprietary interface and therefore do not lend themselves to simple interfacing with a variety of general purpose processor-based systems.
Although a fibre optic ring provides economy if utilized by a plurality of systems, it must be physically coupled to such systems. As the cost of purchasing, placing, and maintaining such a ring is great, even the economy of multi-system utilization generally does not overcome the prohibitive cost of implementation.
A need therefore exists in the art of information communication for a communication system providing cost effective bridging of large physical distances between processor-based systems.
A further need exists in the art for a communication system providing high speed broadband information communication between processor-based systems.
A still further need exists in the art for a communication system and a method of operation which efficiently utilizes the available spectrum in order to provide optimized information throughput.
A need also exists in the art for a fault tolerant communication system providing reliable bridging of physical gaps between processor-based systems.
Additionally, a need exists in the art for a broadband communication system providing simple connectivity to a variety of processor-based systems and communication protocols, including general purpose computer systems and their standard communication protocols.
These and other objects, needs and desires are achieved by a system and method of communication in which a communication array (referred to herein as a hub), is centrally located to provide an air link to a plurality of physically separated subscriber processor-based systems, or other sources of communication such as voice communication, utilizing a communication device (referred to herein as a node, which together with the subscriber processor-based system is referred to herein as a remote system or subscriber system) of the present invention. Preferably, this central array may be physically coupled to an information communication backbone providing communication between air linked systems and physically linked systems. Furthermore, multiple ones of such system may be utilized to bridge large physical separation of systems by the intercommunication of multiple central arrays. Moreover, pervasive surface coverage may be provided by arranging a plurality of such communication arrays to provide a cellular like overlay pattern.
In a preferred embodiment, the communication spectrum utilized by the communication system is frequency division multiplexed (FDM) to provide multiple channels or carriers for simultaneous information communication to a plurality of subscribers. Moreover, a preferred embodiment subscriber system is adapted to be dynamically controllable to select between ones of the FDM carriers utilized by the communication system.
Preferably a carrier frequency in the millimeter wavelength (MM Wave) spectrum, such as 10 to 60 GHz, is used by the present invention. Such carrier frequencies are desirable in order to provide a communication bandwidth sufficient for the transmission of at least 30 Mbps through each defined FDM channel of approximately 10 MHz. However, it shall be appreciated that the concepts of the present invention are applicable to portions of the spectrum other than millimeter wavelengths. For example, the present invention is particularly well suited for use in lower frequency bands, such as those in the 300 MHz to 3 GHz range, where radiation of signals are not as confined to line-of-sight as those of the millimeter wavelength spectrum.
Time division multiplexing (TDM) is preferably utilized to provide multiple, seemingly simultaneous, communications on a single carrier channel. Here ones of the FDM channels are broken down into a predetermined number of discrete time slices (burst periods or timeslots) which form a frame. Each burst period may be utilized by a different subscriber so as to result in information communication contained in a single frame, having a number of TDM bursts, being directed to/from a number of subscribers over a single FDM channel.
Moreover, full duplexing may be synthesized on a single carrier channel by time division duplexing (TDD) through the use of burst periods like those used in TDM. Through TDD, Tx and Rx frames, each frame having one or more burst periods, are defined to provide communication in a particular direction at a predefined time. According to a most preferred embodiment, TDD of the present invention is adaptive (ATDD) to provide for dynamic sizing of the Tx and Rx frames. For example, allocation of burst periods to either a Tx frame or Rx frame may be based on the instantaneous traffic demands of the subscriber systems.
In a preferred embodiment, the central communication array or hub comprises a plurality of individual antenna elements, or other structure, for providing radiation of signals in predefined areas, or antenna beams, having subscriber systems deployed therein. Preferably, the hub is adapted to conduct simultaneous communication with multiple ones of the subscriber systems. Such simultaneous communications may be accomplished using a plurality of FDM channels wherein the channels themselves are sufficiently isolated to allow simultaneous communications at the hub. Additionally or alternatively, the hub may be adapted to provide isolation of FDM channels so as to allow their simultaneous use in communications. Accordingly, signals associated with a particular subscriber system may be communicated on one carrier channel while a signal associated with another subscriber system is communicated on another carrier channel. Where sufficient isolation exists in the simultaneous use of such FDM channels, a preferred embodiment of the present invention provides increased capacity through overlapping radiation of these FDM channels in a same service area.
In the preferred embodiment, wherein ATDD is utilized, the present invention operates to optimize utilization of bandwidth by dynamically allocating spectrum as forward (Tx) and reverse (Rx) link channels depending on traffic demands. However, where insufficient isolation exists between multiple FDM channels in simultaneous use, adjustment of the allocation of forward and reverse links in one channel may interfere with communications in another channel. For example, a first carrier channel Tx frame and Rx frame may be adjusted such that an overlap exists between the transmission of this first carrier channel by the hub with the receiving of a signal by a second carrier channel by the hub.
Accordingly, a preferred embodiment of the present invention operates groups (referred to herein as an interference group) of resources, such as the aforementioned carriers, prone to interference (whether co-channel interference, inter-carrier interference, or the like) for dynamic adjustment of ATDD forward and reverse links. Preferably, the carriers of an interference group are adjusted in xe2x80x9clockstepxe2x80x9d fashion, such that each carrier is operated with a same forward and reverse link time and duration. Accordingly, the asymmetry of the carriers may be dynamic to serve the traffic demands, while avoiding interference between the carriers of an interference group.
Of course, depending upon the particular interference conditions experienced and the communication quality levels tolerable by particular systems, ones of the carriers of an interference group may be adjusted other than lockstep, if desired. For example, operation of the present invention may allow overlapping reverse link communication in one direction of another, or the remainder of the grouped carriers, by ones of the carriers of the interference group (i.e., forward link of carrier A may overlap reverse link of carrier B) while not allowing overlap in the other direction (i.e., reverse link of carrier A may not overlap forward link of carrier B).
A preferred embodiment of the present invention provides for common control of an interference group, such as through a processor based system utilizing forward and reverse traffic demand information (referred to herein as a traffic scheduler), such as may be determined instantaneously, historically, or even predictively, associated with all subscriber systems or other traffic sources assigned to all carriers within the interference group. Accordingly, an instantaneous forward/reverse ratio can be calculated and implemented for the entire group of carriers. Since all carriers within the interference group share common transmit and/or receive timing, operation of this preferred embodiment eliminates the aforementioned interference.
In an alternative embodiment of the present invention a plurality of traffic schedulers, such as one for each carrier, determine the proper instantaneous forward/reverse link ratios. For example, a traffic scheduler for each carrier will analyze forward and reverse traffic demand information for a particular carrier to determine desirable forward/reverse link ratios for use with that carrier. Each such traffic scheduler may also be provided information with respect to other carriers of the interference group, such as through communication with other traffic schedulers and or a centralized controller, analysis of interference experienced on an associated carrier channel, analysis of historical data, and/or the like. Accordingly, the traffic schedulers associated with the carriers of an interference group may each determine the proper forward/reverse ratio to be utilized.
Where carriers of an interference group are utilized to provide communication in a same service area, i.e., radiation of multiple carriers of an interference group overlap, a preferred embodiment of the present invention utilizes frequency-agile subscriber systems to optimize operation. For example, under direction of a traffic scheduler, the subscriber systems may vary the frequency (carrier channel) of operation of its receiver, transmitter, or both to allow the traffic scheduler to balance the instantaneous forward and reverse traffic demands across a plurality of carriers. Accordingly, a plurality of TDD carriers operating in dynamic lockstep asymmetry may be controlled to achieve gains in RF spectrum utilization equal or even better than the same number of carriers operating under independent dynamic asymmetry.
In the above described embodiments, the communication system may utilize an initialization algorithm, perhaps including a token passing arrangement for shared data users, to poll subscriber""s systems and determine communication attributes of each such system as experienced at various resources, such as antenna beams, carrier channels, etcetera, of the central array. This information may be utilized, such as by the aforementioned traffic scheduler, to determine the optimum assignment of resources, including antenna elements, TDM burst periods, FDD frequency assignments, and TDD Tx and Rx time assignments for each such system, both initially (i.e., upon deployment and/or system reconfiguration) and during operation (i.e., under control of traffic schedulers). This information may additionally be utilized to provide secondary assignment of resources to maintain system integrity in the event of an anomalous occurrence, thereby providing system fault tolerance.
A technical advantage of the present invention is provided in that dynamic asymmetry of ATDD communications may be accomplished across a plurality of TDD carriers without introducing interference between/among the carriers.
Another technical advantage of one of the present intention is that full exploitation of the benefits of dynamic asymmetry associated with ATDD are provided.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.